The phrase comes from cap, slang for a lie, and its opposite no cap, meaning to be truthful. The terms spread widely through hip hop lyrics and social media in the late twenty tens before stop the cap became a standalone reaction online. Short voice clips of the phrase were shared on TikTok and soundboards as a quick way to challenge a story without typing an explanation. It remains popular because the meaning is instantly understood and the blunt tone fits comedy edits, gaming clips, and everyday callouts.